Liquid crystal display devices are used as, for example, small display devices such as display sections of mobile phones in addition to display sections of large-screen TVs. TN (Twisted Nematic) mode liquid crystal display devices often used conventionally have a relatively narrow viewing angle. Recently, however, wide viewing angle liquid crystal display devices of an IPS (In-Plane-Switching) mode, a VA (Vertical Alignment) mode and the like have been produced. Among such wide viewing angle modes, the VA mode can realize a high contrast ratio and so is adopted for many liquid crystal display devices.
As one type of VA mode, a CPA (Continuous Pinwheel Alignment mode is known. In a general CPA mode liquid crystal display device, pixel electrodes and unit electrodes having a highly symmetrical shape are provided, and also projections (convexed portions) or openings are provided in correspondence with the centers of the pixel electrodes or the unit electrodes. When a voltage is applied to a liquid crystal layer, liquid crystal molecules are tilt-aligned radially in accordance with an oblique electric field formed by a counter electrode and the highly symmetrical pixel electrodes or unit electrodes. Using the oblique electric field formed by an alignment regulating force of the inclined side surface of the convexed portions or by the openings, the tilted alignment of the liquid crystal molecules is stabilized. Thus, liquid crystal domains centering around the projections (convexed portions) or the openings are formed. In this manner, with a CPA mode liquid crystal display device, the liquid crystal molecules are aligned radially in an attempt to improve the viewing angle characteristics (see, for example, Patent Documents 1 through 3).
In a liquid crystal display device disclosed in Patent Document 1, pixel electrodes are provided in areas defined by gate lines and source lines, and the pixel electrodes each have a plurality of subpixel electrodes (unit electrodes) separated from each other. Storage capacitance lines extending parallel to the gate lines are provided in areas between the plurality subpixel electrodes. A counter electrode includes convexed portions in correspondence with the respective centers of the plurality of subpixel electrodes in an attempt to improve the viewing angle characteristics.
In a liquid crystal display device disclosed in Patent Document 2, pixel electrodes are provided so as to overlap gate lines, and storage capacitance lines extending parallel to the gate lines are each provided between two pixel electrodes adjacent to each other in a column direction. In the liquid crystal display device of Patent Document 2, the pixel electrodes each have a plurality of unit electrodes connected to each other, and a counter substrate includes convexed portions in correspondence with the respective centers of the unit electrodes.
Patent Document 3 discloses a transreflective liquid crystal display device. In the liquid crystal display device of Patent Document 3, a counter substrate includes convexed portions in correspondence with the respective centers of transmissive regions and reflective regions. In the liquid crystal display device of Patent Document 3, a liquid crystal layer is thicker in the reflective regions than in the transmissive regions. Owing to this, the retardation amount in the reflective regions is approximately equal to the retardation amount in the transmissive regions. In the liquid crystal display device of Patent Document 3, the convexed portions provided in the transmissive regions are higher than the convexed portions provided in the reflective regions. Owing to this, the alignment stability and the response speed of the liquid crystal molecules in the respective regions are improved.
As another type of VA mode, an MVA (Multi-domain Vertical Alignment) mode, by which a plurality of liquid crystal domains are formed in one pixel area, is also known. In an MVA mode liquid crystal display device, alignment regulating structures provided on the liquid crystal layer side of at least one of a pair of substrates which face each other with a vertical alignment type liquid crystal layer interposed therebetween. The alignment regulating structure is, for example, a linear slit (opening) or a rib (projecting structure) provided on an electrode. Owing to the alignment regulating structures, an alignment regulating force is supplied from one side or both of two sides of the liquid crystal layer, and so a plurality of liquid crystal domains (typically, four liquid crystal domains) having different alignment directions are formed. In this manner, it is attempted to improve the viewing angle characteristics (see, for example, Patent Document 4).
However, in the liquid crystal display device of Patent Document 4, the alignment regulating force is supplied to liquid crystal molecules by the linear slits or the ribs. Therefore, the alignment regulating force acting on the liquid crystal molecules in the pixel areas varies in accordance with the distance from the slit or the rib. As a result, the response speed of the liquid crystal molecules in the pixels varies. For this reason, a VA mode liquid crystal display device in which the alignment regulating force is supplied to the liquid crystal molecules within a plane of the pixel electrodes by forming the pixel electrodes in a specific shape has been studied (see, for example, Patent Document 5).
In the liquid crystal display device of Patent Document 5, the pixel electrodes having a minute linear pattern (striped pattern) are provided. The linear pattern includes a cross-shaped trunk electrode and linear electrodes extending in four different directions from the trunk electrode. Such a structure of the pixel electrode is called the “fishbone structure”. Storage capacitance lines are each provided so as to overlap a part of the cross-shaped trunk electrode. With the liquid crystal display device of Patent Document 5, when a voltage is applied to a liquid crystal layer, the liquid crystal molecules are aligned parallel to the longitudinal direction of the striped pattern. As a result, a plurality of liquid crystal domains (typically, four liquid crystal domains) having different alignment directions are formed. In this manner, it is attempted to improve the viewing angle characteristics.